This invention relates to a diagnostic method for the production of motor vehicle engines, and more particularly to a method for verifying correct matching of an installed oxygen sensor and a respective engine.
In mass production of motor vehicles, a variety of vehicle types and models are commonly produced on the same assembly line. This can present a problem because many of the components designed for one type or model of vehicle will malfunction or operate incorrectly if installed in a different type or model of vehicle. Accordingly, various precautions must be taken to ensure that the correct components are installed in each vehicle. The focus of this invention concerns engine exhaust gas oxygen sensors. When an assembly line is designed to accommodate both engines configured to run on leaded fuel and engines configured to run on unleaded fuel, two different types of oxygen sensors must be on hand. Unfortunately, it is difficult to distinguish between the two sensor types, and it is possible that the wrong sensor could be installed in a given vehicle. There are various possible arrangements for preventing improper sensor installation, such as providing unique wiring harnesses and/or connectors for each type of vehicle, but such arrangements are undesirable because they increase both component proliferation and cost. Accordingly, what is needed is a method of reliably and cost effectively verifying proper matching of a vehicle engine and its exhaust gas oxygen sensor.
The present invention is directed to an improved assembly method and a corresponding diagnostic method carried out by an electronic engine control module in a factory test setting for reliably and inexpensively verifying correct matching of a vehicle engine and an exhaust gas oxygen sensor installed on an exhaust pipe thereof. According to the invention, heating elements within the oxygen sensors are manufactured so as to exhibit an electrical resistance that is different for each type of sensor. Due to normal part-to-part tolerance variation, the heater resistance of one type of oxygen sensor falls into a first range, and the heater resistance of the other type of oxygen sensor falls into a second range. The electronic control module for each engine is calibrated as part of its overall fuel control calibration to recognize an oxygen sensor current requirement range corresponding to the respective fuel control (i.e., leaded or unleaded). The first and second resistance ranges tend to converge as the temperature of the sensors rise above a given value during operation of the engine, and the electronic control module operates during an initial period of engine operation during factory testing prior to convergence of the first and second resistance ranges to measure the average current supplied to the installed oxygen sensor, and to compare the measured current with the calibrated current requirement range. The comparison is used to set a diagnostic indicator, which is checked to determine if the engine should be directed to the next assembly area or returned to a repair area so that the correct sensor may be installed.